Notorious Grid Bottleneck Spawns Western Blackout

The blackout that squelched power flows to nearly 5 million residents of Arizona, California and northern Mexico last night and shut down California’s San Onofre nuclear power plant may be the latest sign of strain in an outdated U.S. power grid. The incident began during maintenance at a substation in Yuma, Arizona that lies at the center of a sclerotic section of the grid between Phoenix and Tucson—one long recognized as critically congested and thus at heightened risk of failure.

Utility officials have not yet identified an explanation for how the substation work took down such a large grid area, since transmission systems are supposed to have sufficient redundancy to survive the loss of any given line or generator. However, such incidents are not without precedent. In 2008 an engineer with Florida Power & Light blacked out 4.5 million customers in south Florida during work on a substation switch in Miami.

What is clear is that the substation where trouble began last night is located in a sensitive spot. The North Gila Substation operated by Phoenix-based utility Arizona Public Service (APS) is on the eastern edge of a zone extending to the Pacific Coast that the U.S. Department of Energy (DOE) judges to be the second-most congested transmission flow path west of the Rockies. The corridor runs from south-central Arizona to San Diego, and at its heart is a single-circuit 500-kilovolt high voltage transmission line that brings coal-fired power from southeastern Arizona to San Diego.

That single line to San Diego leaves the city highly vulnerable, since California’s environmental policies have shuttered many of southern California’s baseload generating plants. “They rely on imports, and if those imports go offline they have nothing to rely on,” says John Kyei, a former APS transmission planning engineer who is now director of Transmission for Houston-based renewable power developer BP Wind Energy.

In 2008 DOE designated the Arizona-California transmission path as a National Interest Electric Transmission Corridor – a move intended to inspire transmission upgrades to crack open the Arizona bottleneck and secure delivery of the state’s power to the coast. A National Grid Congestion study issued by DOE the next year expressed optimism that new and upgraded lines were on the way, and removed the Phoenix-Tucson area (including Yuma) as a Congestion Area of Concern. But some key projects have since lagged.

DOE expected that one critical connector highlighted by Kyei, a 500-kV link from the Palo Verde nuclear power plant to APS’s now infamous North Gila substation, would be in service by next summer. APS now says via its web site that the line won’t be done before 2014. Kyei calls such delay’s business as usual, thanks to the phalanx of roadblocks – from environmental approvals to funding refusals by state-level public utility commissions with parochial interest – that regularly stretch new line planning in the U.S. to a decade or longer.

Kyei says adding a second circuit to the 500-kV line segment that crosses the California-Arizona frontier will be tougher still, because eliminating congestion equalizes prices on either side. California regulators approved a proposal by utility Southern California Edison to expand the line in 2007, only to see it rejected by the Arizona Corporation Commission.

If that stalemate endures, this may not be the last time that visitors to San Diego’s Sea World amusement park find themselves stuck on a roller-coaster, or that pump failures at treat plants spill sewage into water supplies. There is, however, a chance that federal authorities will step in to force transmission improvements. The Energy Policy Act of 2005 empowers the Federal Energy Regulatory Commission (FERC) in Washington to override opposition from states and push through transmission upgrades within designated National Interest Electric Transmission Corridors.

DOE is currently considering a proposal to also delegate to FERC its power to designate national interest corridors, thus streamlining the process for federal involvement. To date use of the federal power has been blocked by state challenges to the DOE’s designation process – a situation that FERC staff would like to change, according to a policy paper posted last week. As they write: “Clearly, the backstop transmission procedure established by Congress has not yet been effective.”

This post was created for Energywise, IEEE Spectrum’s blog on green power, cars and climate